Bioinspired poly(vinyl alcohol)-silk hybrids: Two-way water-sensitive shape-memory materials

Water-sensitive shape memory polymers have drawn significant attention because water is the safest stimulus for living organisms which is much easier to be performed in biological applications. Inspired by the water-stimulated shape memory behavior of supercontracted spider silks, silk fibroin with beta-sheet structure is introduced into poly(vinyl alcohol) (PVA) to develop a novel shape memory material. Bending test indicated that the addition of the silk fibroin favors good water-induced shape-memory effect (WSME) of the PVA/silk hybrids. More importantly, the PVA/silk hybrids also display two-way WSME, which could mimic the behavior of pine cones to close their scales in a wet state and open them again in a dry state. It is demonstrated that the asymmetric laminated structure of the hybrids could attribute to the two-way shape-memory effect, whereas the competitive hydrogen bonds between silk fibroin and PVA from water as switch, the beta-sheet structure as netpoint and its swelling plasticizing effect are main factors for the water-sensitive shape-memory behavior. These PVA/silk hybrids not only possess biocompatibility and nontoxicity, but also have ease to be fabricated, which are promising in various potential applications such as biological, medical, textile, and toys.